Telephone trunking system.



No. 848,814. PATENTED APR..2, 1907. W. W. DEAN. TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED JULY26. 1902.

2 SHEETSSHEET 1 ya $0 I $6 xv 3? J PATENTED APR. 2, 1907.

W. W. DEAN. TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED JULY 26. 1902.

Z SHEETSSHEET 2.

UNITED sTArns PATENr OFFICE.

WILLIAM W. DEAN, OF CHICAGO, ILLINOIS, ASSIGN OR TO KELLOGG SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS,

A CORPORATION OF ILLINOIS.

, TELEPHONE TRUNKING SYSTEM.

Specification of Letters Patent.

Patented April 2, 1907.

Application filed July 26,1902- Serial N- 117.059-

- a specification.

My invention relates to new and useful improvements in telephone trunking systems adapted for use in connecting telephone-lines together for conversation.

In an application filed by me June 28, 1902, Serial No. 113,581, I have shown and described a trunking system for use in connection with telephone-lines of the -Dunbar or two-wire type in which the cut-off relays are operated over a portion of the talking-circuit. I

My present invention relates to trunkingcircuits designed particularly for use in connecting together lines of the two-wire or Dunbar type above mentioned with lines of a different type, although some of the features of the invention are of a more general application and may be employed with various types of lines.

One feature of my present invention is. to

' provide means for placing the signaling apparatus associated with a trunk in condition to operate by current flowing over a circuit entirely independent of the ground connections which may exist on a subscribers line and which, in case they are present, are apt to be faulty and at which earth-currents are liable to be found.

Other features of the invention willjbe partieularly brought out in connection withthe description and claims.

In the accompanying drawings, which represent my invention, and in which the same reference characters are used to designate like parts throughout, Figure 1 is a diagram showing subscribers lines terminating at different offices with the trunking and other circuits extending between said offices to connect the lines together for conversation; and

Fig. 2 represents a similar arrangement, except that a different called-subscribers line is shown and is equipped with more than one subscribers station and in which a different testing arrangement is provided. Y

Referring to Fig. 1, L designates one of the plurality of subscribers lines terminating at the central office C. This line extends in two limbs 2 and 3 from the subscribers station A to the said central oiiice C, whereit is fitted with suitable answering and multiple jacks or connection-terminals J J At the subscribers station the usual telephone instruments are provided and consist of a transmitter 4, a receiver 5, a ringer or call-bell 6,

and the condenser 7. The switch-hook 8 is adapted in its normal position and when the receiver is placed thereon to open the circuit through the transmitter 4 and receiver 5 and to close it through the call-bell 6 and condenser 7. A retardation-coil 9 is connected at the substation when the hook is raised in parallel with the receiver 5 and condenser 7 to provide a path transparent to steady currents, but opaque to voice-currents. The line conductors 2 and 3 include, respectively, the armatures or springs 10 and ll of the cutoif relay R, which is permanently legged to ground from the sleeve-contacts j of the jacks J J The armature or spring 10 is normally connected with ground through the conductor 12, while the opposite armature 11 is normally connected with conductor-13, containing the line-relay R for the line, said conductor leading to the live or ungrounded pole of the. central battery 13, the opposite pole of which is grounded. The line-relay R controls through its armature the circuit of the line-signal S. The forward contacts 14 and 15 of the cut-off relay R are adapted to connect the jacks and the switchboard-section of the line with the external line-circuit when the said cut-off relay is energized.

At the central oliice C the usual o'perators cord-circuit is provided, said cord-circuit having an answering-plug P and a callingplug P each being provided with a tip-contact p and a sleeve-contact p adapted to register with like contact-surfaces and j in the jacks of the line when the plug is inserted therein. The tip-contacts of the plugs are connected together by means of the tipstrands t and t of the cord-circuit andthe,

interposed condenser 0, while the sleeve-contacts are likewise connected by the sleevestrands s and s and the interposed condenser 0 Aconductor 16 extends from the grounded pole of the battery B to the tip strand t and contains the winding of the tip supervisory relay r associated with the answering-plug P, While the live pole of the battery is connected, by means of conductor 17, with the answering sleeve-strand s and includes the'winding of the sleeve supervisory relay 1' These relays r and r ser e to control the circuitof the supervisory la'mp S associated with the answering-plug P, the former relay serving to normally close said circuit of the lamp, while the latter relay normally opens the same. Thebattery B is associated with the opposite or calling end of the cord-circuit and is connected by conductors 18 and 19 with the tip and sleeve strands t and 8 respectively, the former conductor including the winding of the supervisory relay 1", while the latter conductor includes the similar relay r These relays serve in a manner simi-.

lar to the relays r and 1" to control the circuit of the supervisory lamp S associated with the calling-plug P. i

The relays r and 1" are conveniently referred to as the tip-relays and relays r and 1" as the sleeve-relays, since they are connected with and operated by current flowing over the corresponding strands of the cord-circuit. The tip-strand it of the calling and testing plug P is normally open through the extra sprin or movable contact 20 of the sleeve-relay r ut is adapted to be closed by the said spring and its forward contact 21 when the relay is energized. The back con-' tact 22 of this extra spring 20 is connected through the medium of conductor 23 ,with one sideof thehigh-resistance and high-impedance relay r, known as the test-relay, the other side of which is grounded. The armature of this relay is likewise grounded, and its forward contact is connectedwith the primary winding of the operators inductioncoil 25 by means of conductor 24. The other end of the said primary winding is connected through the medium of conductor 26 to the live pole of the battery B a retardation-coil 27 being included in this circuit. The operators transmitter 28 is joined 011 one side to conductor 26 intermediate her primary coil and the coil 27 and on the other.

side through conductor 29 to ground. A condenser c is included in the operators local circuit to facilitate talking and is connected as shown. The secondary winding of her induction-coil 25 is adapted to be in cluded, together with her receiver 30 and a .condenser c, in a bridge between the strands spring k the sleeve-contact k of said key being connected with battery-lead 26 through wire 26= and resistance 26".

A trunk-circuit is shown extending between the central offices and 0 said trunk-circuit being fitted at the outgoing end with multiple jacks J and J and with a retardation-coil 34, legged to ground from the sleeve side of the circuit. The trunk extends in two limbs and 36 to the central office where it is provided with suitable means for testing the condition of the wanted line, for ringing the desired subscriber, and with signals to enable the operator to properly attend the connection. The tip and sleeve trunk-conductors 35 and 36 terminate at the incoming'oflice in windings w and w ofthe repeating-coil W, and between said windings the trunk-relay '1" is connected, said relay being of hi hresistance.- The opposite windings 112 an 112 of the-repeating-coil W with an inte osed condenser c are connected between t e tip-strand t and the sleeve-spring s of the flexible end of the trunk-circuit, said end being hereinafter referred to as a trunkcord. These strands terminate in the corresponding contacts 1) and p of the trunkplug P. A relay 1' is connected with the sleeve-strand of the trunk-cord by means of conductor 37, leading from the live pole of the batteryB to the point 38 and thence by conductor 39 to one side of the relay 1*, the other side of which is connected by conduct0r 40 with the sleeve-strand s of the trunk-cord at point 41, this relay being therefore adapted -to respond to current in the line when the subscribers telephone is oh the hook, the return path for current being" completed over the tip-strand of the cord-circuit and through the ground branch 42, connected with the tip-strand at point 43. Thus relay 1' when actuated closes through its spring 44 a short circuit of the trunk-relay 1, consisting of the conductors 45 and 46, which deprives the'trunk-relay of operating-current and allows its armature to return to normal position. connected on one side by conductor 47 with the point 38 on the battery-wire 37 and upon the other side by conductor .48, leading to the contact 76* of the ringing key, which is adapted to be grounded when actuated by the conductor 49. The spring 50 of the relay 1- closes through its forward contact a locking-circuit for itself, the said forward contact being connected by conductor 51 A relay 1" is with the conductor 48 at point 52 and the said spring 50 being connected by a ,conductor 53 with the contacts 54 of the plugseat switch, the springs 55 of which are grounded and are separated from the-com tacts 54 when the plug is in the seat. When, therefore, the ringin -key is actuated, a circuit for the relay 1' from the battery B is initially closed through contacts of said key,

and as soon as actuated the locking-circuit is closed through the contacts of the plug seat switch, the plug P being at this time out of the seat and inserted in the jack of the called-subscribers line. connected on one side by conductor 56 with the point 57 upon the main battery-lead 58 and upon the other side by means of conductor 59, leading to the signal-lamp 5", which may be termed the guard and disconnect lamp. The other side of the lamp is connected, by means of conductor 60, with the armature 61 of the trunk-relay r, the back contact of-which is connected by conductor 62 with the backcontact and sprin 63 of the relay 1", which spring is connected with the forward contact of grounded spring of the relay 1-, whereby when the trunkrelay and the relay '7 are deenergized and the relay 7" is energized a path for current is provided through the pilot-relay r" and the signal-lamp S this circuit occurring when the called subscriber has hungup his tele phone and the operator has disconnected the cord-circuit from the outgoing end. The pilot-relay, as is understood, controls the circuit of the pilot-lam S". The forward contact of thetrunk-re ay 1 is joined by conductor 71 to the back contact of the spring 70 of the relay 1' whereby when the trunkrelay is actuated and the relay 1" is deenergized a complete circuit for the lamp 5 and the pilot-relay 1' is closed, this taking place when the connection has been established at the outgoing-end of the trunk and before connection has been made at the incoming end, whereby a call or guard indication is given by th'e said signals: -A ringingsignal S is provided, its circuitzbeing completed over conductor 37 to the point'38, thence by conductor 72 to thepoint 73, and thence by conductor 74. to the lamp S", which is connected u on its opposite side by conductor 75 with t- 1e back contact of the armature of the locking-relay 1", said armature being joined b conductor 76 with point 77 upon the con uctor 69, before described. this arrangement it will be seen that when the relay 1* only is energized a path for current will be completed through the ringing-' lamp 8, which will be lighted. A locking-' relay 1" for the ringing-lamp is connected on ,one side by conductor 78 with the point 73 and upon the opposite side by conductor 79, leading to the orward contact of spring 68 of relay r whereby when the tip-relay 1' is actuated a circuit is initially closed from the batter through said relay to cause it to open the circuit of the ringing-lamp S The same movement of the armature closes a locking-circuit for itself over conductor 80 from conductor 79 through its armature and over conductor 76 through conductor 69 and spring 70 of relay 1' to ground.

A ringing-generator g is provided for the A pilot-relay r" is From trunk-cord and is adapted to be connected with the tip-strand thereof by means of the contact 72/ of the ringing-key. It will be understood that any of the usual manually-operated ringing-keys may be used in which the contacts are all actuated simultaneously by means of the ordinary key-lever. A third contact k may be provided in the sleevestrand ofthe trunk-cord, which when actuated is grounded to provide a free path for the return of the ringing-current in case the subscriber should respond during ringing.

The tip of the trunk cord-circuit is normally connected through the movable contact 81 of the relay r and its normal contact with the conductor 82, leading to the tertiary winding 83 of the operators induction-coil and thence by conductor 84 to the point 85 upon the battery-lead 58, whereby the tip of the plug is normally connected with the live pole of the battery. When the rely r is actuated, the spring 81 thereof is disconnected from the .testm -circuit and, completes throu h itsforwar contact the tip-strand for taTking. The operators transmitter 86 is placed in a local circuit with the primary of the induction-coil and may be charged by means of a local battery. The secondary 87 of her coil is connected in series with her receiver 88 and the condenser 89 in the ordercircuit 33. The telephone-line L terminatin at the central ofiice C is provided at the su station with the usual instruments and with a grounded signaling-bell 6, a local battery 9O bein provided for talking purposes. At the centa office the line is furnished with multiple jacks J and J, as many as desired beiru employed, the ti -spring servin when lifted by means of t e connecting-p ug to close through its associated contacts the 10- cal circuit of the cut-off relay R which to ether and at all times insulated from the ta kin -circuit, are connected with ground through conductor 91, the forward contact and spring92 of the cut-off relay B and through the five-hundred-ohm resistance-coil 93 to ground.

The 0 eratlon is as follows: The A subscriber esiring a connection with a subscriber located at another-exchange removes his receiver from the hook, and thereby closes a ath for current between the limbs 2 and 3 0 his line through the transmitter 4 and retardation-coil 9, thecondenser 7 and receiver 5 being connected in parallel with.

the retardation-coil. The closing'of this cir cuit permits current to flow from the battery B through conductor 13, line-relay R sprin '11 of cut-off relay R, limb 3 of the telep one-line, through the retardation-coil 9 and transmitter 4 at the substation, and

thence over limb 2 back to the central office and spring 10 of cut-off relayR, through conductor 12 to ground. The line-relay R is thus operated and closes the circuit of the signal-lamp 8 to ground from the conductor 13. The operator upon seeing the line-signal exposed inserts the answering-plu P into the answerin -jack J of the subscri%ers line and connects her telephone 30 with the cordcircuit by depressing the listening-key k 7c to receive the order from the subscriber. The insertion of the plug P closes a circuit through the cut-off relay R from the live pole of the battery B through conductor 17, sleeve supervisory relay 1, sleeve-strand s, sleeve-contacts p and j" of the plug and jack, thence through the winding of the cut-off relay R to ground. The operation of this relay disconnects the armatures 10 and 11 from the ground-Wire 12 and from the battery-lead 13 and connects them through the forward contacts 14 and 15 of said armatures .to the normally disconnected jacks J J".

The operation of the supervisory relay 1' over the path just traced serves to close through its armature and front contact the circuit of the supervisory signal S which is associated With the plug P; but it is prevented from glowing by the o eration of the tip supervisory relay 1, whic is connected in the conductor 16 and receives current over telephone-line and the ti -strand t of the cord-circuit and through t e conductor 16 to the grounded pole of the battry B as soon as the cut-off relay R is operated. The su ervisory signal S therefore remains inert w e the battery B furnishes current over the metallic telephone-line for the operation of the supervisory relays and for conversational purposes. The operators transmitter 28 is receiving current at this same time from the battery B over the conductor 26, throu h retardation coil 27, thence through -t 1e transmitter 28 and over conductor 29 to ground. When sound-Waves strike the transmitter 28, the current flowing therethrough is varied, which causes a variation of the charge in the condenser c and a corresponding surge of current through the primary of her induction-coil These induce voicecurrents in the secondary, which are transmitted to the line, and the operator is therefore able to conversewith the calling subscriber.

Upon learning that a subscriber in the exchange (3 is desired the A operator depresses the order-key k to connect her telephone with the order wire or circuit 33 and repeats the number of the Wanted subscriber to the B operator, Whose head-telephone 88 is permanently connected With the said orderwire. The latter operator designates the trunk to be used for the connection and proeeeds to test the condition of the wanted line with the tip of the plug of the incoming trunk named. If the line isidle, the cut-off relay R will not be operated, and the testrings Will be disconnected therefrom, so that a complete circuit for current through the battery B will not be established, and no click will be received by the operator. In case of a connection, however, at one of the jacks of the wanted line the cut-off relay is actuated, and the test-rings 7' are connected to ground. Upon touching the tip of the plug P thereto, therefore, a complete circuit for current from the battery B is provided over conductor 58 84, the tertiary Winding of the operators induction-coil, conductor 82, spring 81 of relay 1'9, and the tip-strand t of the cord and over conductor 91, spring 92 of the cut-off relay 1- and through the resistance 93to ground. The operator will therefore receive a click in her receiver and will- 'ever, that the line is found idle, the plug is inserted in the adjacent jack of the subscribers line and the ringing-key actuated. The actuation of the ringing-key, as before pointed out, connects the generator 9 with the tip side of the line and actuates the callbell 6 at the subscribers station. It also closes the contact if to ground, which actuates the relay r over local circuit from the battery B, comprising conductors 37 and 47, the relayitself, conductor 48, to the ringingkey andthence over contact It? thereof and conductor 49 to ground. As soon as this relay is actuated the locking-circuit before mentioned is closed through its spring 50 and the plug-seat switch, the contacts of the latter being closed to ground owing to the fact that the connecting-plug P has been removed from the seat.

drawn from the line and. placed in the seat.

A testing-circuit is opened by the spring 81- of the relay 7', and the tip-strand of the trunk-cord is completed thereby. Spring 70 thereof closes upon its forward contact, and thereby completes a path for current through the ringinglamp 8*, said path including conductors 37 72 74, the lamp itself, conductor 75, the back-contact armature of the trunkrelay r, conductor 7 6, to point 77, and thence over conductor 69 to the forward contact and spring 70 of relay r to ground. This lamp is therefore lighted and indicates to the operator that the subscriber has not yet responded.

At substantially the same-instant that the plug P is connected with the wanted line the plug P of the cord-circuit at the A olliee is connected with the trunk, with theresult that current flows over the supervisory-relay 1" to disconnect the test-relay 7-" and close the tip-strand of the cord-circuitfor conversa-' tion. Current then flows over the outgoing end and act-uates the trunkrelay 1', which This relay Will thereforeremain actuated during the remainder of the connection or until the plug P is Withopens'the circuit of the disconnecting-lamp S and prevents'its operation at this time.

:The resistance of the trunk-relay is sufficient to prevent the actuation of the tip'supervisory relay r-"in the A cord-circuit, whereby the supervisory lamp' associated therewith remains actuated and indicates to theoperator that the subscriber has not yet responded.

When the called subscriber responds, a path for current through the relay 1' is provided from the live pole of the battery B over conductor '37 to point 38, conductor 39 to the relay 1', and thence over conductor 40 to the sleeve-strand ofthe trunk, and over the sleeve side of the subscribers line to the substation, and back over the ti side of the line and through the tip-stran of the trunk-cord and conductor 42 to ground. This actuatestheIelay T the resistance of which is high to prevent too lar e a current from flowing through the subscri ers instruments and closinga short circuit of the trunkrelay 1. The removal of the resistance of the trunk-relay permits a suflicient flow of current over the A cord-circuit to actuate the supervisory relay 7-, and thereby opening. a

circuit of the supervisory lam S to indicate to the operator that the ca led subscriber has responded. The trunk-relay being deprived of current permits its armature to return to normal osition, which would actuate the disconnctamp S save for the fact that 5. forward contact the initial circuit of the lockits circuit is opened. by the spring 68 of the relay 1". Thespring 68 closes through its ing-relay 1*, said circuit bein completed through the battery B over con uotors 37- 72 78, thence through the locki-n -relay and over conductor 79 to the forwarcontact of spring 68, thence by way of'conductor'69 and spring of relay 'r" to ground; This relay is thus actuated to render the ringing-signal S inoperative and to close its locking-circuit over conductors 80, through its armature, and by way of conductors 7669 andsp'ring' 70 to' ground. This circuit remains closed'throu h the remainder of the connection, or until t e relay 1" is deenergized.

The subscribers are now connected together for conversatiofil The battery. B is furnish ing current to the An-subscribers for talkin and for the-operation of thesu ervisor an .other relays associated therewlth, whi ethe been busy or the subscriber had failed to answer the plug P would have been inserted in one of the jacks J or J of the busyback or dontanswerap aratus. 'These circuits comprise an induct1on-coil 94, having its primary in circuit with the rapidly-rotating circuit-breaker 95 and the battery B this battery being referably the same as battery B though s own separately for convenience. The secondary of the inductioncoil 94 is connected in circuit with the rapid circuit-breaker 94 and the more slowly rotating interrupter 95. From the interrupter 96 a conductor 98 leads to the sleeve-contacts of thebusy-back jacksJ" through a fifty: ohm resistance-coil 99, while interrupter 97 is connected by conductor 100 through the resistance-coil 101 to the sleeves of the dontanswer jacks J The ti 8 of both sets of jacks are united by con uctor-102 with a grounded pole of the battery. The circuitreaker 95 causes induced currents in the secondary circuits, which are interrupted at short intervals by interrupter 96 and at lo er intervals by the interrupter 97 to cause 'stinctive tones at the jacks J 9 and J whereby when a trunkplug 'is inserted in one or the other of the jacks a corresponding signal is transmitted to the waiting subscriber: It will be seen that when a plug is inserted the circuit of the battery B over the sleeve side is interrupted by the interrupter 96 or 97 as the case may be, which alternately energizes and deenergizes the relay 1', whereby supervisory lamp S associated with the A cord circuit, is flashed. At the same'time the distinctive tone caused by the induction-coil. 95 is sent to the waiting subscriber.

' At the termination of the conversation. when the A subscriber returns his receiver to the hook a supervisory si 7 with the A cord-circuit, 1s lighted. When al S associated the subscriber at the A 'oflice hangs up his" telephone, the relay r is deprived of operating-current, which introduces the resistance of.the trunk-relay 1 into the metallic circuit of the out oing end ofthe .trunk, which causes the ighting of the supervisory relay 8 in the A cord, thus indicating to the A operator that the conversation has terminated. The cord-circuit is then disconnected from the trunk, with the result that the trunk-relay is deprived of o erating-current and closes, through its bac contact, the circuit of the disconnecting-lamp S said circuit being completed from the live pole of the battery B over'conductor 58 to oint 57, conductor 56, pilot-relay 1', con uctor 59, disconnect-signal S conductor 60, spring 61 of trunk-relay r conductor 62,spring 68 of relay r conductor 69, and spring 70 of relay 1 to round.- The pilot-signal S is simultaneous y-actuated to attract the attention of the operatorto the disconnect-Si al. The operator at the incoming endo the trunk noticing the disconnect-signal withdraws the trunk-plug from the called line and inserts it in the plug-seat, whereby the locking-circuit for the relay 1' is opened, which restores all parts to normal position. The disconnectsignal S serves also as a guard-lamp in case the A operator inserts the calling-plug P intoa wrong trunk-jack, for the reason that the trunk-relay will be operated, while the sleeverelay is not operated. A circuit will therefor be completed from the live pole of the battery B over conductor 58 to point 57, conductor 56, relay 1*", conductor 59, guardlamp S conductor 60, spring 61 of trunk-relay 1, its forward contact, the conductor 71, and the back contact and spring of relay 7" and thence to ground. The disconnectlamp, as well as the pilot-relay, are therefore lighted and indicate to the operator that a mistake has been made. v

The order-circuit 33, as is indicated by the branch lines 33, connects the B operatorwith several A operators either at the same or different exchanges. The A o erator is also provided with a plurality of eys k to connect herself with the different B operators. The busy back or dont-answer apparatus is common to the various sections of the incoming trunk-board, as is indicated by the radiating lines.

Although I have described the method of making connections through the medium of the order-circuit, I do not wish to so confine the invention, for it is apparent that the A operator is able, by means of her testing apparatus, to test the condition of the several trunks before her until an idle trunk is found.

Upon so testing and finding an idle trunk she may insert the plug P of her cord-circuit,

with the result that the trunk-relay r oper 'callingsignal from the A operator to the .B

operator. The B operator upon seeing the signal S would depress her listening-key m or m which would connect her receiver in series with the repeating-coil windings w and in, these receiver connections being indicated in dotted lines in Fig. 1. She is therefore able to communicate with the A operator. The presence of the condenser. 0 (shown in dotted lines and in parallel with the trunk-relay 1" permits conversation between the operators at this time. Upon learning the desired connection the B oper-. ator completes the circuit, as before described. It will also be understood that had the A subscriber called for a connection with another subscriber in the same exchange the line of that subscriber would have been tested in the ordinary manner by means of the cord-plug B and the test-relay 1*, and the subscriber would have been called by' the ringing-generator g in the usual way.

Fig. 2 shows a similar arrangement of the The trunk-circuit is provided with means for selectively calling the several stations on the line and with testing apparatus to cooperate with a special form of test-contacts employed in connection with the jacks of the line. The cord-circuit with which connection is cstab lished at the outgoing end of the trunk is indicated diflerently, but is supposed to be provided with the same apparatus shown in Fig. 1. In this figure the tip strand of the trunk-cord is normally connected with a testrelay 1" which is of high resistance and impedance to prevent a large variation of cur.- rent on the line tested. The same arrangement of operators circuitis provided as in connection with the cord-circuit shown in Fig.'1. The ringing-generator g is connected, by means of contact h of the ringing-key, with the tip side of the line, while the contact 7L connects the sleeve side of the line to ground to provide a return-path'for current in case the subscriber answers during ring.

ing. A corresponding contact h is provided which grounds one side of the relay r when the ringingkey is operated to actuate said relay. The said. generator can also be connected with the sleeve-spring of the cord by means of the spring 0 of the ringing-key, the tip-spring 0", which is operated at thesame time, being grounded and the spring 0 serving to close a circuit of the relay 1". It will be understood that three springsin each key are operated simultaneously by the usual key-lever. The subscribers stations are provided with apparatus of the same type as shown on line L of Fig. 1, except that the signaling-bell is grounded from one side of the line at one station and from the other side of the line at the other station. At the central office the jacks are'provided with series contacts, whereby the tip side of the line is normally connected from the signaling device S with one pole of the battery B and the sleeve side of the line is normally connected with ground, the contacts in the several connections being carried through theseries contacts 1n the acks when the plug 18 inserted in one of the jacks. The testing-terminals 7' which are also the sleeve talking-terminals,

are connected directly with one side of the talking-circuit, and when a plug is inserted in one of the acks current from the live pole of the batteryjis present at the sleeve and testing contacts. When, therefore, the line is tested and is found busy, a complete path for current is provided from the test-terminal, which is raised to a potential above that of the earth and over the tip side of the line through the grounded test-relay I, which is actuated in the usual way to cause a click in the operators receiver. When the line is found idle, a trunk-plug is inserted and the proper ringing-key is actuated to ring the desired subscriber. The operation of the ring ing key serves to actuate the relay r to v thereby place the signaling and 'other apparatus in condition to operate,as described in reference to Fig. 1. The line-circuit during conversation isunprovided with ground, and no cut-ofi relay isused, the ground at the plug-seat switch serving to cause the necessary operation of the apparatus. Otherwise the construction and arrangement of this figure is the same as in Fig. 1 and is therefore not specifically described, as it will readily be apparent when considered in connection with the description and explanation of Fig. 1. It will be understood that the connecting apparatus of Fig. 2-n1aybe employed in connection with Fig. '1, although where desirable the testing apparatus of Fig. 2 may be used in Fig. 1 also, the different features of Fig. 1 may be used in connection with that of Fig. 2. i r l The ground connections heretofore referred to, it will be understood, may and in practice usually are one and the same, or

they may be the common office-return, and ground connections may be placed at the opposite poles of the several batteries instead of those shown in the diagrams, all of which is apparent to those skilled in the art. The

- resistance of the relay' r may be five hundred ohms, although the proportions may be larger without disturbing the operations of the system. It is also-apparent so far as some features of the invention are concerned that the lines may terminate in single cords and plugs in place of the double cords and plugs described and that the trunks may terminate in jacks in place of the plugs and cords. I do not wish to be limited to the exact ar rangement shown, for it is apparent that imrious changes and modifications maybe made therein and still come within the principle of the invention; but Y What ll do claim, and desire, to secure by Letters Patent, is 1 1.- The combination with a trunk line adapted to connect telephonedines together for conversation, of a signaling apparatus for the incoming end of the trunk, a relay at said end to place said apparatus in conditi'on to operate and adapted to be actuated during connection with the called line and before the called subscriber's response, and-a lockingcircuit for said relay closed by itself when actuated to maintain-the same operated, substantially as described.

2. The combination with a trunk line adapted to connect telephone-lines together for conversation, of -a signaling apparatus for the incoming end, of'the trunk, arelay at said enda'ctuated ovelfla local circuit indesaid second relay over a local circuit independent of the talkingpendent of the talking-circuit and trunk-connecting means, said relay serving to place said apparatus in condition to operate, and a locking-circuit for said relay closed by itself when actuated to maintain the same operated, substantially as described.

3. The combination with a trunk line adapted to connect telephone-lines together for conversation, of a signaling apparatus for the incoming end of the trunk, a relay at said end to place said apparatus in condition to operate, a local circuit therefor, a manually-operated switch independent of the trunk-connecting means to open and close said local circuit, said relay serving when actuated to close a locking-circuit for itself whereby the same remains actuated, substantially as described.

4. The combination with atrunk line adapted to connect telephone-lines together for conversation, of a signaling apparatus for the incoming end of the trunk, a relay at said end to place said apparatus in condition to operate, a local circuit therefor, a ringingkey for the trunk to connect the calling-generator therewith, said key serving to open and close said local circuit, and means to .stantially as described.

6. The combination with a trunk line adapted'to connect telephone-lines together for conversatiomofa relay at the incoming end actuated by current over the trunk from the outgoing end, a second relay at the in coming: end, a signalalso at the latter end whoseactuation de ends upon said relays,- eing initially actuated circuit, and thereafter over a locking-circuit closed by. itself, substantially as described. v 7. The combination with a trunk line adapted to connect telephone-lines, together for conversation, of a relay at the incoming end actuated bycurrent over the trunk from the outgoingend, a second relay at the incoming end,a signal also at the latter end 'whoseactuation depends uponjsaid' relays, a

local circuit for said second relay over which it is initially actuated, a switch independent of the trunk-plug for controlling said circuit, and a locking-circuit for said relay closed by itself when actuated, substantially as described.

, the incoming end of the trunk, a relay to 8. The combination with a trunk line adapted to connect telephone-lines together for conversation, of a relay at the incoming end actuated by current over the trunk from the outgoing end, a second relay at the incoming end, a signal also at the latter end whose actuation depends upon said relays a local circuit over which said second relay is initially actuated, a ringing-key for the trunk to connect the calling-generator there to, said key controlling said local circuit, and a locking-circuit closed by itself to thereafter maintain the relay actuated, substantially as described.

9. The combination with a trunk-line adapted to connect telephone-lines together for conversation, of signaling apparatus for the incoming end of the trunk, a relay at said end to place said apparatus in condition to operate, a locking-circuit for said relay closed by itself when once operated, and a plug-seat switch to open said locking-circuit when the connection has .been taken down and the trunkconnecting plug has been seated there in, substantially as described.

10. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of signaling apparatus at place said apparatus in condition to o erate, a local circuit for said relay indepen ent of the talking-circuit, a manually-operated switch tocontrol said circuit, a locking-circuit for said relay closed by itself when actuated to maintain the'same operated during the connection, and a plug-seat switch con trolling said locking-circuit which is adapted to open the same when the connection has been severed and the trunk-connecting lug placed in the seat, substantially as descri ed.

11. The combination with a trunkcircuit adapted to connect telephone-lines together for conversation, of a signal for the incoming end of the trunk, a relay adapted when actuated to place said signal in condition to operate, a local circuit for said relay independent of the talking-circuit, a ringing-key for the trunk adapted to connect the calling-generator therewith, said ringing-key serving when operated to close said local circuit, a lockingcircuit for said relay to maintain the same operated during conversation and after the ringing-key has been returned to normal position and a plug-seat switch to control said locking-circuit whereby when the connection has been severed and the trunk-connecting plug placed in the seat, the locking-circuit is open, substantially as described.

12. The combination with a trunk-line adapted to connect telephone-lines together for conversation, of a relay at the incoming end of the trunk actuated by current over the trunk from the outgoing end, a second relay at saidend, means for initially operating said latter relay during connection with a called line and before the subscribers response, a locking-circuit for said latter relay 0 therefor closed by itself when actuated, a

plug-seat switch forthe incoming trunk-plug controlling said locking-circuit and adapted when the plug is in the seat toopen the same, and a signal whose actuation depends upon said two relays, substantially as described.

14. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of' a relay at the incoming end actuated by current from the outgoing end, a second relay at the incoming-end actuated over a local circuit, a manually-operated switch inde endent of the trunk-connecting plug to c ose said circuit, a lockingcircuit for said latter relay, means to 0 en said circuit when the connection is ta (en down, and asignal whose actuation depends upon said two. relays,.substantially as described.

15. The combination with a trunk-circuit adapted to connect subscribers lines together for conversation, of a relay at the incoming end actuated by current from the outgoing end, a second relay at the incoming end, a local circuit therefor independent of the talking-circuit, a ringing-key to connect the call ing-generator with the incoming end of the trunk, said key'serving when actuated to close said local circuit, alocking-circ'uit for the relay closed'by itself when actuated, a plug-seat switch haying contacts in said locking-circuit and adapted to normally open same, whena trunk-plug is seated therein and a signal whose actuation depends upon said two relays, substantially as described.

16. The combination with a trunk-line adapted to connect telephone-line circuits together, of a ringing-signal for the incoming end of the trunk, a relay actuated over a local circuit distinct from the talking-circuit to direct current through said signal to operate the same when the subscriber has been called but before his response, a ringing-key to connect thecalling-generator with the incoming end of the trunk, said key serving to close the circuit of said relay to actuate the same, a second relay adapted to deprive said signal of operating-current when the subscriber responds, and a third relay for locking out said signal and means for maintaining actuatingcurrent through said relay during the remainder of the connection, substantially as described.

17. The combination with a trunk-line ad apted to connect subscribers lines together for conversation, of. a ringing-signal for the incoming end of the trunk, a relay adapted to direct current through said signal to operate the same when the subscriber has been called but before his response, the circuit of said relay being initially closed before the subscriber responds and thereafter controlled through a' locking-circuit to maintain the I same operated during the connection, a sec- 0nd relay adapted to deprive said signal of operating-current when the called subscriber responds, and means for locking out said signal during the remainder of the connection, substantially as described.

18. The combination with a trunk-line adapted to connect subscribers lines together for conversation, of. a ringing-signal for the incoming end of the trunk, a relay adapted to direct current through said signal before the called subscriber responds, a local circuit for said relay initially closed in the operation of the ringing key of the trunk, said relay being adapted to close a locking-circuit for itself when actuated, a plug-seat switch in said locking-circuit adapted to open the same when the trunk-plug has been returned to normal position, a second relay adapted to deprive said signal of operating-current when the; called subscriber res onds, and means for locking out said signa during the remainder of the connection, substantially as described.

19. The combination with a trunk-line adapted to connect telephone-lines together independent of the talking-circuit for placing said'signal in condition to operate, said loca circuit being closed by a switch independent of' the trunk-connecting plug, and further means controlled by the connection at the outgoing end of the trunk for rendering'said signal inoperative, substantially as described.

20. The combination with a trunk-line adapted to connect tele honelines together for conversation, of a isconnect-signal'for the incoming end of the trunk, a relay actuated by current over a local circuit for placing said signal in condition to operate, said local circuit being controlled by the trunk ringing-key, and a relay actuated by current over the outgoing end of the trunk when the connection exists at said outgoing end to prevent said signal from operating, substantially as described 21. The combination with a trunk-line adapted to connect telephone-line circuits together for conversation, of a disconnectsignal for the incoming end, a relay actuated over a local circuit initially closed by the trunk ringing-key when operated to call the wanted subscriber, said relay serving to place said si nal in condition tooperate, a locking-circuit for said relay closed when the relay is once actuated, a plug-seat switch in said locking-circuit to open the same when the connection is taken down and the trunkplug is placed in the seat, and a relay energized by current over the trunk from the outgoing end when connection'exists at said end. to prevent said signal from operating, substantially as described.

22. The combination of a trunk-line, of a cord-circuit to connect with its outgoingend and a called subscriber's line with which its incoming end is adapted to connect, a signal associated with the incoming end, a relay also at said incoming end adapted to be operated by current sent over the trunk-circuit, a second relay at said incoming end adapted to be operated by current flowing over a local circuit, a ringing-key initially controlling said local circuit, said circuit being thereafter controlled through contacts of said relay to maintain the relay operated, a plugseat switch to open the locking-circuit of said relay when the trunk-plug is returned to normal position, said relays jointly controlling the said signal so as to operate the sanie to 9 give a guard indication when the cord-circuit is connected with the trunk-circuit and the trunk-circuit is disconnected from the said line, or to place said signal in condition to operate so as to give a disconnect indication when the cord-circuit is disconnected from the trunk and the trunk is connected with the line, substantially as described.

23. The combination with a trunk-line, of

'a cord-circuit to connect with its outgoing end, and a called subscribers line with which its incoinlng end is adapted to connect, a guard-signal for the incoming end of the trunk, means to actuate said signal by current sent over the trunk when the cord-circuit is connected with the trunk, and further means actuated by current sent over a local circuit when the trunk is connected with the called line to render said signal inert, said local circuit being independent of the trunkconnecting plug, substantially as described.

24. The combination with a trunk-line, of a cord-circuit to connect with'its outgoing end, and a called subscribers line with which its incomin end is adapted to connect, a guardsigna for the incoming end of the trunk, means to actuate said signal by current sent over the trunk when the cord-cir- .cuit is connected with the trunk, and further means actuated by current sent over a local circuit when the trunk is connected with'the called line to render said signal inert, said, local circuit being closed through contacts of the trunk ringing-key, substantially as described.

25. The combination with a trunk-line, of a cordcircuit to connect with its outgoing end, and a called subscribers line with which its incomin end is adapted to connect, a guard-signal for the incoming end of the trunk, means to actuate said signal by current sent over the trunk when the cord-circuit is connected with the trunk, and further means actuated by current-sent over a local circuit when the trunk is connected with the called line to render said signal-inert, said circuit being initially controlled through contacts of the ringing-key and thereafter completed through contacts of the plug-seat switch, substantially as described.

26. The combination with a trunk-line adapted to connect telephone-lines together for conversation, of a si end of the trunk, a relay actuated during connection with the called line and before the subscribers response to place said signal in condition to operate, a second relay actuated by current from over the trunk when a connection exists at the outgoing end thereof, of a third relay at said incoming end connected with the sleeve-strand of the cord-circuit and res onsive to current in the line when the ca ed subscriber answers, said relays serving to control said signal in such manner that when the first relay is energized and the other relays deenergized, the signal is actuated, substantially as described.

27. The combination with a trunk-circuit 'nal at the incoming.

adapted to connect subscribers lines together, a supervisory signal associated with the outgoing end of the trunk, a highresistance trunk-relay at the incoming end, said relay being normally dis osed in the path of current over the trunk to imit the flow therein, and thereby permit the operation of said supervisory signal, a relay at the incoming end of the trunk connected with the sleeve strand thereof, and responsive to current in the line when the called subscriber answers said relay serving to remove the resistance of the trunk-relay to permit an increased flow of current over the trunk to thereby render said supervisory signal inoperative, substantially as described; Y

2-8.. In a telephone system, the combination with a telephon'eJine, of atrunk-circuit adapted to be connected therewith, of a ringing-si nal at the incoming endo'fthe trunk 3 1n condition tooperate by current sent through a local circuit independent of 1 place the talking-circuit by the actuation of the ringing-key, and again rendered inoperative by current flowing over a o'rt-ion of the talking-circuit when the cal ed subscriber answers his call, substantially as described.

' Signed by meat Chica o, county of Cook,

State of Illinois, this 23d ay of July, 1902.

' 7 WILLIAM W. DEAN.

Witnesses:

ROBERT LEWIS AMES, GAZELLE BEDER. 

